There exists a general problem of being able to obtain uninterrupted operation and maximum throughput in a singling station to which sheet material to be singled is fed in the form of bundles that possibly arrive irregularly. It is obviously rather unsuitable to use for this purpose transport systems that transport a stack to be singled to the singling unit only when the latter has finished singling a current stack. Such solutions can be realized economically due to the simple coordination of the bundle logistics, but in practice they have a considerably limited throughput which is restricted by the feed time of the next stack to be singled to the singling unit. Developments of this principle reduce interruption times by faster feed of further stacks, but they likewise settle for suboptimal throughput rates dependent on the feed speed, and cause additional downtimes due to the increased transport speed—possibly due to displacements of stacks—which results in increased maintenance effort.
DE 195 12 505 A1 from the applicant describes a method for continuous singling of stacks of sheets which avoids the stated disadvantages of fixed-cycle solutions. During singling of a stack of loose sheet material, a further stack is fed in such a way that it can be grasped and singled without interruption by the singling unit after processing of the first stack. Since singling now does not have to be interrupted for providing the next stack, uninterrupted operation is possible.
Continuous feed of stacks of sheets to the singling unit is ensured by the interaction of two rake-shaped feeding elements which alternately take over a stack from a likewise rake-shaped deposit area and transport it from a deposit position on a feeding path to a singling position where it can be singled by the singling unit. After a stack has been singled sheet by sheet by the singling unit, the corresponding feeding element must be returned from the singling position to the deposit position for receiving a further stack already waiting on the deposit area. Since the other feeding element is already located in the singling position at this time to ensure continuous singling, the first feeding element cannot be returned on the feeding path, but must be returned on a parallel path outside the feeding path. For this purpose, the rake-shaped feeding element is drawn out of the feeding path and guided parallel thereto to a position adjacent the rake-shaped deposit area. Since the prongs of the feeding element interact with the prongs of the deposit area in such a way that the feeding element can be inserted into the deposit area laterally from the adjacent position, the feeding element to be returned is finally inserted into the deposit position where, by a new motion on the feeding path, it takes over the stack lying ready on the deposit area and feeds it to the singling unit.
The transport system of DE 195 12 505 A1 thus requires substantially three elements, the immovable deposit area and two similar, vertically and horizontally movable feeding elements which alternate permanently between the deposit position and the singling position through an uninterrupted loop motion. The disadvantage to be mentioned for this concept is the complex constructional principle which, for checking the multiaxial motion of each feeding element in agreement with the position of the other feeding element, requires the use of a multiplicity of position sensors and a control electronics which coordinates the loop motions of the feeding elements. The complex construction increases production costs and leads to increased maintenance effort and therefore to increased operating costs and possibly downtimes. Moreover, in the case of faster singling units or small stack sizes, supply problems are conceivable since, for maintaining continuous singling, the long motion paths of the feeding elements must be covered in a shorter time than the singling unit requires for singling a stack.
Starting out from DE 195 12 505 A1, the invention is based on the problem of proposing a method for continuous singling of sheet material which is based on a simple constructional principle and which allows fast feeding of stacks to be singled.